The Controller Area Network (CAN), as well as an extension of CAN referred to as “time triggered CAN” (TTCAN), are known, for example, from standards of the ISO 11898-1 to -5 family; these are also referred to hereinafter as “standard CAN.” The media access control method used in CAN is based on bitwise arbitration. In bitwise arbitration, several subscriber stations can simultaneously transfer data via the channel of the bus system without thereby disrupting data transfer. The subscriber stations can furthermore, upon transmission of a bit via the channel, ascertain the logical state (0 or 1) of the channel. If a value of the transmitted bit does not correspond to the ascertained logical state of the channel, the subscriber station then terminates access to the channel. With CAN, bitwise arbitration is usually performed on the basis of an identifier within a message to be transferred via the channel. Once a subscriber station has completely transmitted the identifier onto the channel, it knows that it has exclusive access to the channel. The end of the transfer of the identifier thus corresponds to a beginning of an authorization interval within which the subscriber station can exclusively use the channel. According to the CAN protocol specification, other subscriber stations are not allowed to access the channel, i.e. transmit data onto the channel, until the transmitting subscriber station has transferred a checksum field (CRC field) of the message. A point in time at which transfer of the CRC field ends thus corresponds to an end of the authorization interval.
Bitwise arbitration thus results in nondestructive transfer, via the channel, of that message which has won the arbitration method. The CAN protocols are particularly suitable for transferring short messages under real-time conditions; by appropriate allocation of the identifier, it is possible to ensure that particularly important messages almost always win the arbitration and are sent successfully.
The increasing networking of modern vehicles and the inclusion of additional systems to improve, for example, driving safety or driving convenience, is accompanied by rising demands in terms of the data volumes to be transferred and the latency times permissible in the context of transfer. Examples are vehicle dynamics control systems such as the electronic stability program (ESP), driver assistance systems such as automatic cruise control (ACC), or driver information systems such as traffic sign detection (see, for example, descriptions in “Bosch Kraftfahrtechnisches Handbuch” (Bosch motor vehicle technology manual), 27th edition, 2011, Vieweg+Teubner).
German patent document DE 103 11 395 A1 discusses a system in which asynchronous serial communication can occur alternatively via an asymmetrical physical CAN protocol or via the symmetrical physical CAN protocol, and a higher data transfer rate or data transfer security for asynchronous communication is thereby achievable.
German patent document DE 10 2007 051 657 A1 discusses using an asynchronous, fast, non-CAN-conforming data transfer in the exclusive time windows of the TTCAN protocol in order to increase the transferred data volume.
In “Overclocking of controller area networks” (Electronics Letters, Vol. 35, No. 22 (1999), p. 1924), G. Cena and A. Valenzano discuss the effects of overclocking the bus frequency in sub-regions of messages to the data rate that is effectively achieved.
It is apparent that the existing art does not provide results that are satisfactory in every regard.